Some electronic components, particularily solid state active devices such as diodes, transistors, and integrated circuitry, are adversely affected by heat. Their electrical characteristics undergo large relative change at temperatures in the range just above room temperatures. As a consequence, it is common in the design of electronic apparatus to attempt to keep the temperature of such devices as cool as possible. They often generate heat at a rate that requires conduction cooling rather than mere convection cooling. Heat is conducted from the device to a heat sink which is cooled by convection and radiation. The effectiveness of the attempt to move heat from the device to the heat sink depends in part upon the cross-sectional area of the conductive path and that depends in part upon the degree of smoothness of the surfaces at the interface between the device and its sink. Heat sinks are usually made of metal. When the device must be insulated electrically from the sink, a layer of mica or other insulating material is interposed between them. In that case, the effective area of the heat conducting path depends upon the degree of smoothness of four surfaces rather than two. Any surface irregularities result in voids at the interface across which little heat is conducted.
To provide a high degree of smoothness at the interface is costly and may be impractical. The practical alternative has been to make a paste of a semi-liquid carrier and powders of heat conducting material. That paste is applied on one or more of the mating surfaces between the device and its heat sink and insulator.
The common vehicle is silicone grease. This works well, but it is messy and it contaminates equipment, work stations and clothing, and cannot be completely removed as it is not soluble. It is so messy that getting production workers to use it is an industry-wide problem. One alternative is to use a gasket of polymeric material, often silicone rubber, in which a heat conductive material has been suspended. That alternative works in some cases, but it requires the use of heavy fastening elements and heavy torquing which, in some cases, does not fill the resulting voids. This invention provides a better solution. A solution that costs less, works just as well, and that does not have the disadvantages of past materials and processes.